1. Field of the Invention
The present invention relates to rear-projection film with “day/night” effect comprising at least two layers, where the film comprises at least one grey layer comprising at least one thermoplastic with transmittance of from 10% to 70% in the visible wavelength range and at least one layer comprising at least one thermoplastic and scattering particles, and also to the use of the said films as rear-projection areas in the vehicle interior sector.
2. Description of Related Art
Rear-projection displays are considered to be an alternative to TFT/liquid-crystal displays and to be a technology of the future for vehicles. Diffuser films have been disclosed as projection films, but in particular for laser light sources do not give adequate brightness and especially exhibit undesired speckle characteristics.
Speckles are problematic bright spots of light which arise when coherent light is incident on a rough surface and is reflected. The same effect is also observed on transmission of laser light through rough, scattering surfaces or on transmission through materials which comprise scattering particles.
This phenomenon is caused by constructive and destructive interference of coherent light, by virtue of the different optical path lengths resulting from the scattering. The resultant statistical distribution of the interference effects, which appear as bright spots on a dark background, therefore alters not only with the properties of the light source but also with the scattering geometry, the position of the observer and the optical characteristics of the observer.
Known diffuser films provide opaque white or diffuse-matt white surfaces which do not suit the design of dashboards and centre consoles. Combination with “day/night” surfaces is an essential factor in harmonizing the claimed rear-projection films with the surfaces.
The prior art has disclosed Vikuiti™ rear-projection films as described in WO 1998/45753 A1, where glass beads have been applied on an acrylate film and the interstices/intermediate layer between beads and film has been filled with black dye. The beads focus the projected light and the black dye absorbs ambient light.
Disadvantages of the said films are the high manufacturing cost with use of the glass beads, the weight of these, and the fact that there are restrictions on the geometric spatial design of these films, since the precise arrangement of the glass beads permits only a certain curvature of the underlying film.
U.S. Pat. No. 8,284,487 B1 discloses a rear-projection screen composed of a plurality of projection tiles bonded to one another via adhesive and via a flexible film. The disadvantage of the said arrangement is the existence of seams and the restrictions in the spatial arrangement of the tiles.